1. Field of the Invention
The present invention relates to a feed for larvae of crustaceans (except for artemia) such as lobsters, crabs, earshells (awabi) and sea urchins and shellfishes which are important marine resources.
2. Related Art Statement
All over the world inclusive of Japan, culture fishery and breeding have showed marked technological advancement with the yield increasing steadily year by year.
In culture fishery and cultivation fields, however, a number of factors concerning the feeding and breeding of fry and small fishes at the initial stage considered of the most importance are still unclarified, partly because they are very minute individuals. Considerable difficulty involved in the production of feed formulations accommodative to minute individuals stands in the way of any fruitful studies of nutritional and other requirements.
For the reasons as mentioned above, the breeding at this state often relies upon long experiences and the so-called "the sixth sense". As a matter of course, this results in lowerings of the yield and noticeable variations in the annual yield.
For instance, floating and deposited diatoms belonging to Skeletonema and Cheatoceros are now widely used as the optimum feeds for natantia peneus larvae (of the zoeal and mysis stages). Difficulties are encountered in the stable cultivation of diatoms, because they grow at a low rate, are affected by weather, and tend to be easily contaminated by other organisms.
Substituent feed formulations for diatoms have recently been studied. However, it is difficult to triturate and regulate such feed formulations to a size of 5 to 50 microns that is the size of diatoms. Another disadvantage of such feed formulations is that, even though they are regulated in size, their particles are so fine that their contents are readily soluble in breeding water, leading to not only ready losses of nutritive value but also marked contamination of the breeding water.
Further, for the production of seedlings for shellfishes such as Pleurotomaria nordotis, Temnopleuroida pseudocentrotus, Pleurotomaria sulculus and Ostracea crassoster, diatoms are used as the feeds at their larval stage. However, since the production of diatoms is uncertain in itself as mentioned above, there are raised problems of low yield rate in breeding of larvae and deviation in the yield.
Still further, such shellfishes take in floating diatoms and, then, deposited diatoms over a period of several months. However, it has been found that the production of such deposited diatoms requires much more labor and time, and undergoes much larger weather influences, than does the production of floating diatoms.